The present invention relates to a low-pressure rare gas discharge lamp with a rare gas sealed therein as a light emitting gas. Particularly, the present invention is concerned with a low-pressure rare gas discharging fluorescent lamp for use in office automatic (OA)-related machinery and apparatus such as facsimiles and copying machines.
As the prior art, for example on pages 1079-1082 of "Toshiba Review", Vol. 40, No. 12 (1985) there is described a low-pressure rare gas discharge lamp with several ten Torr to several hundred Torr of xenon sealed therein in place of mercury used in ordinary fluorescent lamps. More particularly, since mercury vapor is used in ordinary fluorescent lamps, this vapor pressure changes with change of the ambient temperature, and light output also varies, while the use of xenon is advantageous in that the light output does not vary over a wide temperature range because mercury is not used. This advantage is utilized to attain the extension of use as a light source for OA-related machinery and apparatus.
On the other hand, for example, as reported by Mr. Okuno of Matsushita Electric Industrial Co., Ltd. at the 1975 national meeting of the illumination society, it is known that in a xenon-sealed low-pressure rare gas discharge lamp, the best light emitting efficiency is realized by making the sealed gas pressure extremely low, not higher than 0.1 Torr. However, as also pointed out by the same report, there has been the problem that in such a low pressure region, xenon is extinguished by a clean-up phenomenon during discharge and the service life of the lamp expires in a short time.
Thus, in a low-pressure gas discharge lamp, if the sealed gas pressure is set low, there will be an increase of luminance and improvement of efficiency, but the life of the lamp will expire in an extremely short time due to a clean-up phenomenon. Therefore, in order to ensure the service life of the lamp it has inevitably been required to increase the gas pressure under the sacrifice of luminance and efficiency.